The essential functions of a ski binding are to firmly maintain a ski boot in place on a ski during the normal use of skis and to disengage a ski boot from a ski, whenever a user has bumped against something or fallen down in any manner specifically in any direction at any speed and the like. The former function is required to allow a user to control skis under his desire, and the latter function is required to protect him against injury, such as fracture, sprain, dislocation and the like.
To satisfy these two conflicting independent requirements, the ski bindings in the prior art are designed to elastically clamp the toe and the heel of a ski boot with a ski. More specifically, the toe clamp is provided with an upper clamping member which clamps the front top edge of a ski boot downward, and a pair of side clamping members or jaws each of which elastically clamps the corresponding front side edge of a ski boot inwardly in the horizontal direction and disengages the same, whenever the front side edge of a ski is urged sideways with an amount of energy sufficient to displace the corresponding side clamping member or jaw outwardly beyond a predetermined amount of length or angle. The heel clamp is provided with a vertical clamping member which elastically clamps the rear top edge of a ski boot downward in the vertical direction and disengages the same, whenever the rear top edge of a ski is urged upward with an amount of energy sufficient to upwardly displace the corresponding vertical clamping member beyond a predetermined amount of height or angle. The heel clamp is sometimes provided also with a pair of side clamping members each of which elastically clamps the corresponding rear side edge of a ski boot inwardly in the horizontal direction and disengages the same, whenever the rear side edge of a ski is urged sideways with an amount of energy sufficient to outwardly displace the corresponding side clamping member beyond a predetermined amount of length or angle. It is clear, therefore, that the function of a ski binding available in the prior art inevitably depends on the displacement of or the energy absorbed in one or more elastic members employed for the ski binding.
In order to control skis or change the sliding direction of skis, a torque which is usually called "Fersen Schub" (heel thrust) in Germany is required. This heel thrust must be applied to a point of ski which is located apart from the point where the combined snow resistance is applied to a ski, which is located around the center of the entire length of a ski contacting the surface of snow but which moves back and forth depending on the snow conditions and the like. Incidentally, the point at which this heel thrust is applied moves depending on the forward inclination of a user but is approximately located slightly ahead of the heel. The distance between the point where the combined snow resistance is applied to a ski and the point where the heel thrust is applied to the ski is the length of arm which determines the amount of the torque. On the other hand, since the heel thrust is applied to a ski through the point which connects the ski boot and the ski, the heel thrust of course functions to disengage the toe clamp and/or the heel clamp.
Therefore, it is clear that such a ski binding as depends on the displacement of one or more elastic members is involved with adverse effects for controlling skis, because a powerful control of skis frequently results in unexpected disengagement of a ski boot from a ski. Therefore, a tendency is observed to set the tension of the elastic toe and/or heel clamping members, such as springs, as large as possible for the purposes to reduce the displacement of the elastic members and to reduce possibilities of unexpected disengagement of a ski boot from a ski. As a result, the heel vertical clamping member is inclined to be set not to disengage a ski boot from a ski, unless a force as high as 50 through 200 Kg is applied between the heel and the heel vertical clamping member to cause a displacement in the magnitude of 10 through 20 mm for the heel. The corresponding figure for the heel horizontal clamping member or the toe horizontal clamping member is 20 through 80 Kg. These figures are extremely high from the view point of safety, because some parts of the human body can not endure even 5 Kg. This tendency can be a parameter causing injury such as fracture, sprain, dislocation and the like for any body including experts and beginners.
Incidentally, however, it is true that any of the conventional ski binding of which the function predominantly depends on the displacement of elastic members sufficiently functions or safely disengages a ski boot from a ski, if some or all of the elastic members are urged with the sufficient amount of energy to cause a predetermined magnitude of displacement for the corresponding elastic members, without giving an abnormally large amount of force to any part of the user's body. This means that any of the conventional ski binding functions well, whenever a user has bumped against something or fallen with a speed in excess of a predetermined amount which is involved with a predetermined amount of kinetic energy enough to cause some of the clamps to function. However, whenever a user has bumped against something in a strange manner or fallen at a relatively small speed which corresponds to an amount of kinetic energy less than that which is enough to cause one of the clamps to function, there is a large possibility that the ski binding does not disengage a ski boot from a ski. Mostly in such a case, despite the fact that the user has a marginal amount of kinetic energy due to his speed, an injury occurs, because he has a considerable amount of potential energy which is equivalent to the kinetic energy involved with the speed in excess of 10 Km/hour and which is enough to cause injury to some part of his body, depending on the manner in which the energy is applied to the specific part of his body.
Accordingly, it has been determined that the ski binding available in the prior art and which utilizes one or more elastic members can safely disengage a ski boot from a ski, in the event that a user particularly an expert has fallen at a relatively high speed. However, the conventional ski binding has a tendency not to disengage a ski boot from a ski in the event that a user, particularly a beginner, has fallen at a slow speed, potentially causing injury depending on the manner of his fall. Therefore, albeit the ski binding in the prior art may be safe for experts, it is not necessarily safe for beginners.
On the other hand, most of the heel clamps in the prior art have a shape to partly surround a heel in order to firmly clamp the heel. As a result, such heel clamps are scarcely allowed to move sideways, and such ski bindings disengge a ski boot from a ski only in the case where the toe is rotated beyond a predetermined amount of angle centering around the heel as the pivot. For example, when a user tries to change the sliding direction of skis, he applied a heel thrust (Fersen Schub) to the skis from left to right with his heel, and the combined snow resistance is applied to the center of the entire length of a ski contacting the surface of snow, from right to left. Therefore, these two forces function to displace the right toe clamping member. If, at this time, a shock is applied at the front end of a ski from right to left, this shock functions in the same direction as the above mentioned two forces, resultantly causing the right toe clamping member to quite easily disengage the ski boot from a ski, despite the fact that the user does not to intend or desire. Therefore, a stronger tension is required for toe clamping members to reduce the possibilities of this type of unintentional disengagement of a ski boot from a ski. This of course causes an adverse effect for safety. In other words, if a sufficient magnitude of safety is required, sufficient magnitude of control can not be obtained, and if a sufficient magnitude of control is required, a sufficient magnitude of safety can not be obtained.